OP FISHES. 



37 



SCHEME OF THE CIRCULATION OF THE BLOOD IK FISHES 



A A. The gills, 'the fringes of which are the extreme 

 terminations of arteries. 



B. The ventricle of the heart, or forcing pump, which 

 drives the blood into a single artery, that soon divides into 

 two principal branches, carrying the blood equally to the gills, 

 on each side of the head. 



C. The oracle of the heart, or receiving organ, into which 

 the veins empty the blood which has been the round of cir- 

 culation. This contracts, and throws its contents into the 

 ventricle, and that, again, forces it onward into the gills. 



D. The main artery of the heart, or branchial artery, anal- 

 ogous to the pulmonary artery of breathing animals. 



E. Refers to the branchial veins, which carry the blood 

 that has been exposed to the action of the water, in the gills, 

 back into the body, and pours it into the great tube lying un- 

 der the back-bone. 



F. This is the vessel into which all the renewed blood is 

 emptied — which is an artery, acting like the left side of 

 the heart in warm blooded animals ; when it contracts, or 

 pulsates, it throws its contents through all the small vessels 

 that branch from it, into and over every portion of the body. 



heart exerts its muscular force in throwing gru- 

 mous blood, which has been the round of circula- 

 tion, to the gills, and no further. From these, it 



